203

链表基础操作

class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        while (head!=NULL&&head->val==val)
        {
            ListNode* temp=head;
            head=head->next;
            delete temp;
        }
        ListNode* cur=head;
        while (cur!=NULL&&cur->next!=NULL)
        {
            if(cur->next->val==val){
                ListNode* temp=cur->next;
                cur->next=cur->next->next;
                delete temp;
            }else{
                cur=cur->next;
            }
        }
        return head;
        
    }
};

707

多写多试

class MyLinkedList {
public:
    struct LinkedNode
    {
        int val;
        LinkedNode* next;
        LinkedNode(int val):val(val),next(nullptr){}
    };
    MyLinkedList() {
        head=new LinkedNode(0);
        size=0;
    }
    
    int get(int index) {
        if(index>(size-1)||index<0){
            return -1;
        }
        LinkedNode* cur=head->next;
        while (index--)
        {
            cur=cur->next;
        }
        return cur->val;        
    }
    
    void addAtHead(int val) {
        LinkedNode*newNode=new LinkedNode(val);
        newNode->next=head->next;
        head->next=newNode;
        size++;
    }
    
    void addAtTail(int val) {
        LinkedNode*newNode=new LinkedNode(val);
        LinkedNode* cur=head;
        while(cur->next!=nullptr){
            cur=cur->next;
        }
        cur->next=newNode;
        size++;
    }
    
    void addAtIndex(int index, int val) {
        if(index>size)
        return;
        if(index<0)
        index=0;
        LinkedNode*newNode=new LinkedNode(val);
        LinkedNode* cur=head;
        while(index--){
            cur=cur->next;
        }
        newNode->next=cur->next;
        cur->next=newNode;
        size++;
    }
    
    void deleteAtIndex(int index) {
        if(index>=size||index<0){
            return;
        }
        LinkedNode* cur=head;
        while(index--){
            cur=cur->next;
        }
        LinkedNode* temp = cur->next;
        cur->next = cur->next->next;
        delete temp;
        temp=nullptr;
        size--;
    }

private:
    int size;
    LinkedNode* head;

};

206

利用双指针法，画图理解

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* temp; 
        ListNode* cur = head;
        ListNode* pre = NULL;
        while(cur) {
            temp = cur->next;  
            cur->next = pre; 
            pre = cur;
            cur = temp;
        }
        return pre;
    }
};